Fiber optics transmission has a characteristic that high speed transmission is available without being affected by signals of other lines. Therefore, the fiber optics transmission is also used for not only a communication network provided by a common carrier but also for connection between modules of a super computer that needs high-speed parallel transmission of data.
In the fiber optics transmission, as for the connection between optical transmission and optical reception devices, one-to-one connection by optical fibers is a basic configuration. Therefore, in the case where a plurality of nodes of computers are connected by parallel transmission using optical fibers, for example, when the number of optical interfaces of the computers increase, the number of optical fibers also increases in proportion to it. Also, it was necessary for optical fibers to be connected to optical switches in order to connect among a large number of optical interfaces, and thus there have been cases where a structure of optical transmission lines are complicated.
On the other hand, an optical space transmission system is known as a communication configuration capable of high speed transmission without laying optical fibers (refer to e.g., patent literature 1: JP 2004-080253).